1. Field of the Invention
This invention relates generally to igniters for gaseous fuel, and more particularly to igniters that include igniter elements and shields for protecting the igniter elements.
2. Background
Igniters, particularly, non-pilot light igniters, have been used in industrial and domestic gas burning appliances such as gas-fired furnaces, stoves, clothes dryers, and the like.
FIG. 1A shows a conventional igniter 100, which includes an igniter element 106 essentially disposed within an igniter shield 101 (see also FIG. 1B) for protecting the igniter element 106. Typically, the igniter element 106 is a ceramic igniter element, such as that disclosed in U.S. Pat. No. 5,892,201 (xe2x80x9cthe ""201 patentxe2x80x9d) issued Apr. 6, 1999, to Croucher et al., and assigned to Saint-Gobain Industrial Ceramnics; Inc., Worcester, Mass., USA. That patent discloses inter alia a ceramic igniter element that includes a pair of conductive, end portions coupled to a highly resistive middle portion (also known as a xe2x80x9chot zonexe2x80x9d). When the conductive end portions of the ceramic igniter are connected to respective leads and a voltage is applied thereto, the hot zone of the ceramic igniter rises in temperature, thereby radiating sufficient energy for producing stable, high temperatures suitable for igniting the gas.
Similarly, the igniter element 106 includes conductive end portions (not shown) coupled to a hot zone (not shown). Specifically, the conductive end portions of the igniter element 106 are connected to respective leads 110. A portion (not numbered) of the igniter element 106 with the leads 110 connected thereto is normally cemented within a ceramic sleeve (also known as a xe2x80x9cblockxe2x80x9d) 108, thereby allowing the remaining portion (not numbered) of the igniter element 106 to extend from one end (not numbered) of the block 108. Further, the leads 110 pass through the length of the block 108 and extend from the opposite end (not numbered) of the block 108.
Accordingly, when a suitable voltage is applied across the leads 110, a current flows from one of the leads 110 to one of the conductive end portions of the igniter element 106; through the hot zone of the igniter element 106, thereby causing the temperature of the hot zone to rise; to the other conductive end portion of the igniter element 106; and, then to the other lead 110.
Because conventional igniter elements may be subject to damage or breakage, the igniter 100 is provided with the shield 101. For example, as shown in FIG. 1B, the conventional shield 101 is typically stamped out from metal sheet stock, which is usually a high temperature metal alloy. Specifically, the shield 101 includes a first portion 102a and a second portion 102b, with a pair of slots 105 formed between the first and second portions 102a and 102b. 
After the shield 101 is stamped out from the metal sheet stock, the first and second portions 102a and 102b of the shield 101 are typically formed into substantially tubular sections, as shown in FIG. 1A. The insulative block 108 is then press-fit into the second tubular portion 102b of the shield 101, thereby causing the igniter element 106 to be disposed within the first tubular portion 102a of the shield 101.
As shown in FIG. 1B, a plurality of randomly spaced holes 104 is typically formed through the first portion 102a of the conventional shield 101. Accordingly, when the igniter element 106 is disposed within the first tubular portion 102a of the shield, as shown in FIG. 1A, gas and air (not shown) surrounding the igniter 100 can flow through the plurality of holes 104 to the igniter element 106, thereby facilitating subsequent ignition of the gas.
However, it has now been recognized that the conventional igniter 100, as shown in FIG. 1A, can have certain drawbacks. For example, because the process for manufacturing the shield 101, including the steps of setting-up the tooling required for making the shield 101, stamping out the shield 101 from the metal sheet stock, and forming the first and second tubular portions 102a and 102b of the shield 101, is relatively expensive to implement, the shield 101 substantially increases the cost of the igniter 100.
In addition, in some applications, insufficient amounts of gaseous fuel and air surrounding the igniter 100 flow through the plurality of holes 104 formed in the shield 101 to the igniter element 106, thereby causing the igniter element 106 to fail in successive attempts to ignite the gas. The lack of cooling airflow to the igniter element 106 also frequently causes the igniter 100 to overheat and subsequently burnout prematurely, thereby increasing the cost of using the igniter 100.
It would therefore be desirable to have an igniter including an igniter element and a shield for protecting the igniter element from accidental damage or breakage. Such an igniter would be relatively inexpensive to manufacture and use. It would also be desirable to have an igniter including an igniter element and a shield for protecting an igniter element that has improved ignition characteristics.
The present invention provides an igniter, including an igniter shield with at least one opening formed therethrough marked by a spiral pattern, for improving ignition characteristics of a shielded igniter element and increasing the lifetime of the igniter. The present invention also provides a simplified process for manufacturing the igniter that is relatively inexpensive to implement.
According to a first embodiment of the present invention, an igniter includes an igniter element adapted for igniting gaseous fuel; and, a tubular shield for protecting the igniter element, the igniter element being disposed along the longitudinal axis of the shield, wherein the shield includes at least one opening therethrough forming an oriented spiral passageway.
According to a second embodiment of the present invention, an igniter includes an igniter element for igniting gas; and, a coil or spring-type element for protecting the igniter element, the igniter element being disposed on the longitudinal axis of the spiral coil.
According to a third embodiment of the present invention, an igniter includes an igniter element for igniting the gas; and a cylindrical, insulative sleeve for protecting the igniter element, the igniter element being axially disposed in the sleeve, wherein the sleeve includes as least one hole formed therethrough for exposing a portion of the igniter element to the gas.
The shields of the present invention protect the igniter element from undesired damage and breakage, and allow an optimal flow of gas and air to the igniter element, thereby facilitating subsequent ignition of the gas. The optimal cooling airflow toward the igniter element also prevents overheating of the igniter element, thereby increasing the useful lifetime of the igniter.
According to a fourth embodiment of the present invention, a method of manufacturing an igniter includes stamping out a shield from metal sheet stock; forming the shield into a substantially tubular section; and, disposing an igniter element on the longitudinal axis of the tubular shield.
Other aspects of the invention are disclosed infra.